The ultrasonic inspection of materials for detection of defects is well-known. Scanners using linear array transducers have normally been used in an immersion tank with the linear array transducer submerged in water. Such systems have normally been operated in the pulse-echo mode which requires only an array transducer.
Laminated structures such as those including honeycomb are highly attenuating and thus require higher ultrasonic energy to inspect the parts, particularly for separated lamination areas. This makes through-transmission inspection a more practical method. To build a scanner for through-transmission inspection for immersion inspection would be impractical because a large complex scanning mechanism and tank would have to be built to accommodate large composite laminated structures now being fabricated. In addition, honeycomb structures tend to float and this provides an additional handling problem.
Conventional scanners were generally made to scan in both the X and Y directions, the scanning being along a line in each direction.
A search of the patent literature discloses apparatus and methods which propose solutions for ultrasonic inspections. For example, U.S. Pat. No. 2,751,783 to Erdman discloses a stream of liquid coupling medium employed in a direct line and forming an uninterrupted liquid bridge between an ultrasonic transducer and a test object, the stream carrying consecutively both the transmitted and reflected signals.
U.S. Pat. No. 3,745,833 to Armstrong discloses a thickness gauge for determining the position of a surface of a workpiece. The device has a housing shaped to constrain water to flow coaxially into the upper end of a tube 15, FIG. 3, which is spaced slightly from the inner surface of the housing, and water flows downwardly through a flow alignment member in the tube, the member comprising a cylindrical block 19 having a number of axially extending cylindrical bores 20. Laminar flow is developed in the tube 15 and the cylindrical bores 20.
U.S. Pat. No. 3,908,445 to Verdon et al provides an ultrasonic transducer in a sleeve with flow straightening means downstream of the transducer for producing substantial laminar flow of water at the outlet of the sleeve. The flow straightening means comprises a bundle of tubes which fill the sleeve section. In order to maintain a positive water flow pressure within the outlet end of the sleeve, and thereby prevent cavitation, the outlet end is provided with a flow restrictor shaped to disturb laminar flow conditions as little as possible.
U.S. Pat. No. 3,910,104 to Davies provides an array of ultrasonic transducers, the length of the array of transducers being greater than the width of a plate being tested.
The following additional patents found in the search disclose nozzle constructions of general interest:
U.S. Pat. No. 3,255,626, W. R. Van Der Veer PA1 U.S. Pat. No. 3,303,691, L. Beaujard et al PA1 U.S. Pat. No. 3,420,097, J. Battermann et al PA1 U.S. Pat. No. 3,485,088, D. T. O'Connor PA1 U.S. Pat. No. 3,501,947, M. J. Hetherington PA1 U.S. Pat. No. 3,625,051, Sutekiyo Uozumi PA1 U.S. Pat. No. 3,662,590, Shiraiwa et al PA1 U.S. Pat. No. 3,741,003, W. A. Gunkel PA1 U.S. Pat. No. 3,946,599, J. Patt PA1 U.S. Pat. No. 4,033,178, Holt et al PA1 U.S. Pat. No. 4,164,150, Ries et al PA1 U.S. Pat. No. 4,167,880, L. W. George PA1 U.S. Pat. No. 4,403,510, deWalle et al PA1 Australia No. 255,105, Taylor PA1 French No. 1,275,693, U.K. Atomic Energy Authority